Radio interferenceproof insulator



Patented Jan. 15, 1935 UNiTED STATES PATENT OFFICE 1,9ss,369 RADIOINTERFERENCEPROOF INSULATOR v Application November 12, 1931, Serial No.5744545 4 Claims.

The invention relates to insulators for supporting electricaltransmission lnes.

It is well known that present insulator units cause radio disturbanceswhile Operating at- 5 normal voltage by creating a noise which isaudible directly by the human ear and which is quite noticeable and infact extremely objectionable in radio receivers. The disturbances arenot limited to any certain definite frequency !but range !rom the lowaudible noise to the high radio trequencies. ,It an insulator known tobe creating a disturbance is viewed in the dark a glow or coronaformation is visible, the corona generally Iorming first between the tiewire and the porcelain as the flux through the air gap at this point isthe largest contributing interterence factor. Prior to the' advent otradio and television such discharges were-orno signiflcance but have nowassumed great importance.

It is with the above facts in view that I have devised the presentinvention which has for its general object the provision of a novelinsulating unit which will not cause any disturbances 'which willinterfere with radio reception.

An important object of the invention is to provide an insulator unit ofsuch construction that the s'tresses in the electrical field about itwill be balanced, or in which the electric stresses about the lineconductor and the ground side of the insulator will be so distributedthat the transmission of electric energy through urban and ruraldistricts'may be accomplished without any annoying disturbances to or inradio and television receivers located in the vicinity, that is to saynear overhead electric circuits.

Another object oi the invention is to provide a so-called radio-prec! ornon-interfering insulator which may be used in the same manner asordinary equipment, that is to say ot such de- 4 sign that the usualsupporting pins can be used and the same method employed of securing theline conductor to the insulator, and moreover of such form that theelectrical characteristics, such as dry and wet flash-over values, willbe about the same as tor present units, and the mechanicalcharacteristics unimpaired.

My invention is based principally upon the discovery that substantiallvspherical opposed 50 the interposed dielectric material will avoid theconcentration of electrical stresses and effect such distribution of thelines ot force through the insulator and in the electro-static fieldabout it that !ormation ot corona, with the objection- 66 ableconsequent dlsturbances, will be prevented surtaces on the necessarymetallic elements and until the flash-over voltage of the particularinsulator is substantially reached.

A more specific object of the invention is to provide an insulator unitin which the same number of dielectric and metallic parts may be used ascustomarily and in which the external shape may likewise conform togenerally accepted standards, the construction being moreover applicableto insulators of the pin, suspension, pedestal or other types andregardless of whether there be but one or several dielectric parts. i

An additional object is to provide an insulator construction which willbe simple and inexpensive to make and assemble, positive in action,emcient and durable .in service, and a general improvement in the art.

To the attainment of the foregoing and other objects and advantages, theinvention preferably consists in the details of construction and thearrangement and combination of parts to be hereinafter more fullydescribed and claimed, and illustrated in the accompanying drawing inwhich:

The figure is a view partly in side elevation and partly in sectionshowing the invention.

At the very outset, it should be understood that while I have shown andwill describe the invention as embodied in insulators oi' the typeadapted to support line wires bound in place by so a tie wire, clamp orthe like, there is no limitstion in this respect as the form disclosedis simply by way ot illustration.

Referring more particularly to the drawing,

I have shown the insulator as comprising a dielectric body 10, usuallyof porcelain, which may be plunged, cast or shaped in any other mannerand which, i! of porcelain, is glazed, fired and otherwise treated inthe usual or any prei'erred manner, all of which steps are old and 40well known in the art. The body 10 is represented as having a centralrecess 11 surrounded by a depending petticoat 12 ,outwardly of whichthere may be provided any necessary or desir-, able number of skirts 13.Moreover there is no necessity of using a single dielectric body as usemay be made of several secured together in a well known manner.

The recess 11 is disclosed as cylindrical throughout its major portionbut formed with a spherically curved inner or upper end 14, and locatedwithin this recess is one of the electrodes here represented' as aspecies of metallic or other conducting member ot a more or lessthimble-like form and including a cylindrical u shank portion 15terminating in a spherically curved head 16, the latter being fairlyclosely accommodated within the spherically-curved inner or upper end ofthe recess. This metallic or other conducting member is secured in placeas for example by means of a mass of cement 17 which is a commonexpedient in insulator construction. The present invention is netconcerned with whether the inner surface of the recess be sanded orotherwise roughened or be simply left unglazed or be positively treatedin some manner to insurean adequate grip for the cement, but all ofthese possibilities are contemplated as being within the purview of theinvention. In the present instance the metallic member is shown ashaving a thre'aded opening 18 therein for mounting upon a supporting pinor the like but whether or not this exact scheme is followed dependswholly on the type of insulator in which the invention is to beembodied.

Secured in opposed relation to the metallic member 15 is a conductingcap 19 here shown as having a line wire receiving groove 20 and a tiewire groove 21 though these features are not limitative. These twoelectrodes are of course separated by the interposed dielectricmaterial. A feature of prime importance is that the undersurface 22 ofthe electrode 19 is spherical in shape and is secured, as by cement 23,or the like, within a recessed or sunken portion in the top of the body10, this recess having a spheric'al surface 24 opposite to andpreferably at least substantially concentric with the spherical surface14. While the spacing between these opposed spherical surfaces may bevaried there should be suificient separation that corona will not 'occuruntil the flash-over or puncture values are almost reached.

It will be observed that the exterior surface of the insulator, ordielectric portion thereof, is smooth and unbroken, the exterior surfaceof the lower portion of the cap 19 constituting a continuation of theadjacent exterior surface of the dielectric body. It will also be notedthat the tie wire is in intimate contact with the cap or upper electrodeand consequently in good electrical contact with the spherically curvedelement.

From the above it will be apparent that my construction will permit orbring about the balanced distribution of stresses, by means of thespherical or ball-like electrode in conjunction with the concaved cap.This will be effective in reducing disturbances and will have theadvantage of but little cantilever action on the pin and supporting armtherefor. i

In the new scheme an equalization of stresses is provided so no coronaand discharging occurs until excessive overstressed potentials areapplied. For instance the corona point was increased from about 6 kv. ina present 20,000 volt design to about 25 kv. for the new arrangement.The interference factor of safety for this particular unit was overthree.

Particular attention was given to the design for the fiux distributionfor -the dielectric circuit. For the sphere design for both the pinportion and the cap portion of the new design, the equipotentialsurfaces between the two conducting substances are practically spheres.The metallic or conducting spheres in the porcelain are separatedproperly so corona will not occur until near the flash-over or puncturevalues.

Since the air is one dielectric between the upper electrode (cap of theinsulator) and the lower electrode (the sphere with the threads) and theporcelain is another dielectric the two are combined in multiple. Thedesign of the contour of the insulator is so arranged that the divisionbetween the dielectrics is normal to the lines of force, as near aspractical, and the stress on either side is about the same as it wouldbe were` the other not present.

The electrodes are also so proportioned and shaped and also theporcelain is so shaped that one dielectric does not overstress another.This 'is especially important in these insulator designs wheredielectrically Weak air of low permittivity is necessarily incombination with dielectrically strong insulation of high permittivity.

The differences of permittivity of the air and porcelain is taken careof so that each part is stressed in proportion to its respectivestrength. The insulation of the highest permittivity is placed where thefield is the densest.

Slight alterations from the above mentioned incorporated ideas must bynecessity be modified in order to provide proper leakage and flash-overconditions by the addition of skirts. Larger size porcelain insulatorsnecessitate multipiece designs. Mechanical strength requirements alterthe smooth electrode surfaces which of course would otherwise -be betterfor even flux distribution.

Something further is gained by using more porcelain in the dense fieldssuch as near the conducting cap at the surface and cutting away, as itappears, in the middle of the surface perimeter so as to provide inseries, between some of the fiux lines the insulation of highpermittivity and air of low permittivity;

From the foregoing description and a study of the drawing it will beapparent that I have thus provided a simply constructed and easilyassembled, insulator which by virtue of the relative character andcooperation of the opposed electrodes or metallic inserts willefiectually balance and distribute the stresses' in the electrical fieldabout an insulator and make the flux of the lines of force through rthedielectric uniform, thereby avoiding any concentration of stresses andpreventing the formation of corona with the consequent generation ofdisturbances of diiferent frequencies. -It is thought that theconstruction, operation and advantages should i be readily apparent toone skilled in the ar without further explanation. While I have shownand described the preferred embodiment of the invention, it should beunderstood that the disclosure is merely an exemplification of theprinciples involved as the right is reserved to make all such changes inthe details of construction as will widen the field of utility andincrease the adaptability of the device provided such changes constituteno departure from the spirit of the invention or the scope of the claimshereunto appended.

Having thus described the invention, I claim: 1. An insulator of thenon-strain type comprising a preformed dielectric body provided at itsunderside with an inwardly extending cavity having a substantiallyspherically curved bottom, said body having its top formed with a recesshaving a wall substantially concentric with the 'bottom of the cavity, ametallic thimble secured within the cavity and having a substantiallyspherical head, said thimble having means for engagement upon a pin, anda metallic cap secured within said recess with its exterior surfaceflush with the body.

2. An insuiator ot the non-strain type comprising a dielectric 'bodyincluding a central stem portion and an outwardly extending skirt, saidstem portion being formed at its bottom with an inwardly extendingcavity having cylindricai sides and a spherical bottom, a :metal thimblecemented within said cavity and having a substantially spherical headlocated within the bottom thereof, said thimble having means forengagement upon a pin, the top o! the body being formed with a recesshaving the major portion of its bottom sphericai and concentrie with thebottom of the cavity and having the outer edge portion of its bottomlocated above the junctre of said skirt with the stem and reverselycurved. and a metaliic cap cemented within the recess and having itsouter surface flush with'the adjacent outer surface o! the body.

3. A porcelain insulator ot the cap and pin type, comprising a porcelainbody having an outstanding skirt and a cylindricai central portiontormed with an inwardly extending cavity having a substantiallyspherical bottom, a metallic member having a spherical head located andSecured within 'the bottom of the cavity 'and adapted for engagementupon a pin, the top o! the body being formed with a reeess' of greaterdiameter than the cavity and having a convexly curved sphericai bottomextending to a point above the innermost portion of said skirt, theremaining or outer portion of the -bottom of said recess being reverselycurved, and a metaliic cap seated and Secured within said rcess torelectro-static cooperation with said head.

4. An insulator comprising a preformed dielectric body provided at itsunderside with an inwardly extending cavity having a substantiailysphericaliy curved bottom, said body having its top formed with a recesshaving a wall substantialiy concentric with the bottom of the cavity. ametallic member secured within the cavity and having a substantiallyspherical head fltting within the bottom oi' the cavity, and. a metaliicmember Secured within said recessand having its exterior surface flushwith the body.

HAROLD H. BROWN.

